1. Field of the Invention
This invention relates to a runway for a conveyor using linear motors and which is suitable for use in a clean room which must be free from dust.
2. Prior Art
In semiconductor (such as LSI, super LSI, etc.) manufacturing plants, medicine manufacturing plants, etc., it is a fact that with the recent automation of dust-free workshops, dust-free conveyors between processes and between processing machines have been put to practical use.
As an example of such a dust-free conveyor, there is a system whereby a pallet on which articles for transportation are loaded is floated in the air by compressed clean air discharged from nozzle holes made on the surface of a runway and is transported by thrust imparted thereto by a linear motor provided in the runway.
In the runway, which is an important component of the above dust-free conveyor, there are provided linear motors which impart thrust to the pallet and air ducts for floating the transporting pallet in the air from the surface of the runway.
Since this runway uses linear motors and is a floating-in-the-air system, it must be long and requires precision of processing. In order to meet these requirements, as shown in FIG. 4 the construction of a conventional runway comprises two components, one being a table 21 forming the upper part of the runway and the other being a groove-shaped channel 22 with its upper part opened. These two components are combined to form the runway. The reason why the runway is composed of two different components is that while the table 21 requires a precise finish, the duct or channel 22 does not require such precise finish. Therefore complicated processing operations are required to make the runway, with the result of a high manufacturing cost. Moreover, in order to reduce the weight of the runway, while the table is made of light metal, such as an aluminum alloy, with open spaces 23 made by scooping, the duct 22 is made of steel from the cost point of view.
However, in the above construction, due to limitations of accuracy of measurement, the runway must be assembled with joints and therefore time is required for rectifying differences in level of abutting surfaces at each joint. In addition, since the runway is a combination of different materials as mentioned above, temperature differences are caused between the different materials due to heat generation of a linear motor provided in the grooveshaped duct 22, and deformation of the combined members due to a difference in the coefficients of thermal expansion of the different materials caused by thermal expansion of the runway or by variations in ambient temperature makes it difficult to maintain airtightness in the duct, with a resultant increase in air consumption.
Especially, the provision of linear motors in the runway has great effect on the thrust of the motors and the exposure of the linear motors makes it impossible to provide a necessary open space between the transporting table and the runway and reduces the floating effect. Moreover, manual operations are required for combining the table and the groove-shape duct.
In view of the above disadvantages of the conventional runway, the object of the present invention is to provide a runway which is characterized in that it does not include different kinds of metal or other materials. Open spaces for air ducts and an open space for installation of linear motors are provided separately, but the runway is made as a simple body for the purpose of decreasing air consumption, reducing in weight, facilitating the installation of the linear motors and enhancing the operation of the linear motors.